1. Field of the Invention
The present general inventive concept relates to a nozzle plate for an inkjet head, and more particularly, to a nozzle plate for an inkjet head, which includes an ink-repellent coating layer having high durability, and a method of manufacturing the same.
2. Description of the Related Art
An inkjet head is an apparatus that ejects very small droplets of printing ink on a printing medium in a desired position to print an image in a predetermined color. Inkjet heads may be largely classified into thermal-drive inkjet heads and piezoelectric inkjet heads according to link election mechanism. The thermal-inkjet head produces bubbles using a thermal source and ejects ink due to the expansive force of the bubbles. The piezoelectric inkjet head applies pressure generated by deforming a piezoelectric material to ink and ejects the ink due to the generated pressure.
FIG. 1 is a cross-sectional view of a conventional piezoelectric inkjet head.
Referring to FIG. 1, a manifold 11, a plurality of restrictors 12, and a plurality of pressure chambers 13 are formed in a flow path plate 10 and constitute an ink flow path. A vibrating plate 20 is adhered to a top surface of the flow path plate 10. The vibrating plate 20 is deformed due to the drive of a piezoelectric actuator 40. A nozzle plate 30 having a plurality of nozzles 31 is adhered to a bottom surface of the flow path plate 10. Meanwhile, the flow path plate 10 may be integrally formed with the vibrating plate 20. Also, the flow path plate 10 may be integrally formed with the nozzle plate 30.
The manifold 11 is a path through which ink is supplied from an ink storage (not shown) to the respective pressure chambers 13. The restrictors 12 are paths through which ink is supplied from the manifold 11 to the respective pressure chambers 13. The pressure chambers 13 are arranged on one side or both sides of the manifold 11 and are filled with ink to be ejected. The nozzles 31 are formed through the nozzle plate 30 to be connected to the pressure chambers 13, respectively. The vibrating plate 20 is adhered to the top surface of the flow path plate 10 to cover the pressure chamber 13. The vibrating plate 20 is deformed due to the drive of the piezoelectric actuator 40 and provides a pressure variation required for ejecting ink to the respective pressure chambers 13. The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43 that are sequentially stacked on the vibrating plate 20. The lower electrode 41 is disposed on the entire top surface of the vibrating plate 20 and functions as a common electrode. The piezoelectric layer 42 is disposed on the lower electrode 42 over the respective pressure chambers 13. The upper electrode 43 is disposed on the piezoelectric layer 42 and functions as a drive electrode for applying a voltage to the piezoelectric layer 42.
In the inkjet head having the above-described construction, the surface treatment of the nozzle plate 30 directly affects the ejection performance of the inkjet head, for example, the straightness and ejection velocity of droplets of ink ejected via the nozzles 31. That is, in order to improve the ejection performance of the inkjet head, an inner wall of the nozzle 31 must be ink-philic, while the surface of the nozzle plate 30 outside the nozzle 31 must be ink-repellent. Specifically, when the inner wall of the nozzle 31 is ink-philic, the inner wall of the nozzle 31 makes a small contact angle with ink, so that the capillary force of the nozzle 31 increases. Thus, a time taken to refill ink can be shortened so that the ejection frequency of the nozzle 31 can be increased. Also, when the surface of the nozzle plate 20 outside the nozzle 22 is ink-repellent, the surface of the nozzle plate 20 can be prevented from being wet with ink so that the straightness of ejected ink can be ensured. Thus, a coating layer formed of an ink-repellent material is formed on the surface of the nozzle plate 30 outside the nozzle 31. Perfluorinated silane is widely used as the ink-repellent material because it is known that perfluorinated silane lowers the surface energy of the nozzle plate 30 to minimize ink-wetting.
Meanwhile, an ink-repellent coating layer formed on the surface of the nozzle plate 30 should satisfy the two following requirements. First, the ink-repellent coating layer must make a large contact angle with ink. Second, after ejecting ink, the contact angle of the ink-repellent coating layer with the ink must be maintained constant in time. In other words, the ink-repellent coating layer should have high durability.
FIG. 2 is a cross-sectional view of a conventional nozzle plate used for an inkjet head, and FIG. 3 is a magnified view of region “A” shown in FIG. 2.
Referring to FIGS. 2 and 3, a nozzle plate 30 includes a silicon substrate 32 through which a nozzle 31 is formed, a thermally oxidized silicon layer 34 formed on a surface of the silicon substrate 32, and an ink-repellent coating layer 38 deposited on the thermally oxidized silicon layer 34. The ink-repellent coating layer 38 is formed of perfluorinated silane. The thermally oxidized silicon layer 34 is formed on the entire outside surface of the silicon substrate 32 including an inner wall of the nozzle 31. Also, the ink-repellent coating layer 38 is formed on the thermally oxidized silicon layer 34 formed on the silicon substrate 32 outside the nozzle 31. In the nozzle plate 30 having the above-described construction, since the adhesion of the ink-repellent coating layer 38 formed of perfluorinated silane to the thermally oxidized silicon layer 34 is weak, the performance of the ink-repellent coating layer 38 is very likely to deteriorate over time.